This invention relates to an aluminum electrolytic capacitor suitable for low-voltage use that contains ammonium difluoroacetate dissolved in either ethylene glycol or an ethylene glycol-butyrolactone mixture both containing water and having a room-temperature resistivity of 150 ohm-cm or less and a -40.degree. C. resistivity of less than 11,000 ohm-cm.
Low-voltage capacitors, and particularly those of 16 volt or lower rating, need to retain at least 70% of available capacity at -40.degree. C. To ensure this capacity retention, it is necessary for the electrolyte used to have a room-temperature resistivity below 300 ohm-cm and a -40.degree. C. resistivity below 12,500 ohm-cm. Since the -40.degree. C. resistivity is the critical parameter, an electrolyte with -40.degree. C. resistivity values of less than 11,000 ohm-cm and particularly 8000 ohm-cm or lower is desirable to provide a capacitor that will retain 70% capacitance at this low temperature.
Amine salts of fluoroacetic acid have been used as solutes in electrolytes with room-temperature resistivities of approximately 200 ohm-cm for electrolytic capacitors for low-voltage service. The free acids have also been used.